Research in semiconductor nanowires has been fueled by their unique optical, electronic, and mechanical properties and their potential use in optoelectronic devices, chemical and biological sensors, computing devices, and photovoltaics (Law, M.; Goldberger, J.; Yang, P. D. Ann. Rev. Mater. Res. 2004, 34, 83). Semiconductor nanowires have been synthesized under a wide range of conditions, from high temperature (<1100° C.) gas-phase reactions to relatively low temperature (>250° C.) solution-phase conditions (Law, M.; Goldberger, J.; Yang, P. D. Ann. Rev. Mater. Res. 2004, 34, 83; Hu, J. T.; Odom, T. W.; Lieber, C. M. Accts. Chem. Res. 1999, 32, 435; Trentler, T. J.; Hickman, K. M.; Goel, S. C.; Viano, A. M.; Gibbons, P. C.; Buhro, W. E. Science 1995, 270, 1791; Yu, H.; Li, J. B.; Loomis, R. A.; Gibbons, P. C.; Wang, L. W.; Buhro, W. E. J. Am. Chem. Soc. 2003, 125, 16168; Fanfair, D. D.; Korgel, B. A. Crystal Growth & Design 2005, 5, 1971). Solution-phase routes to semiconductor nanowires are particularly interesting due to their potential for good size and shape control, chemical surface passivation, colloidal dispersibility, and high throughput continuous processes.
Nanocrystals and nanowires of Group IV materials, such as C, Si and Ge, have been extremely challenging to synthesize in solution due to their high crystallization energy barrier, and the propensity of those elements to form stable oligomeric species with hydrocarbons. In the past, crystalline Si and Ge nanowires and multiwall carbon nanotubes have been fabricated using supercritical solvents that are heated well above their boiling points to temperatures between 350° C. and 650° C. by pressurization (Holmes, J. D.; Johnston, K. P.; Doty, R. C.; Korgel, B. A. Science 2000, 287, 1471; Hanrath, T.; Korgel, B. A. J. Am. Chem. Soc. 2002, 124, 1424; Lee, D. C.; Mikulec, F. V.; Korgel, B. A. J. Am. Chem. Soc. 2004, 126, 4951). These temperatures exceed the decomposition temperatures of organosilane and organogermane precursors and the Au:Si and Au:Ge eutectic temperatures (˜360° C.), making it possible to promote Au nanocrystal-seeded nanowire growth (Shah, P. S.; Hanrath, T.; Johnston, K. P.; Korgel, B. A. J. Phys. Chem. B 2004, 108, 9574). Although very high quality nanowires are obtained, it would be more desirable to synthesize crystalline nanowires under milder conditions to alleviate solvent decomposition and safety concerns.